/*
** $Id: lgc.c,v 2.37 2005/12/22 16:19:56 roberto Exp $
** Garbage Collector
** See Copyright Notice in lua.h
*/

#include <string.h>

#define lgc_c
#define LUA_CORE

#include "lua.h"

#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"


#define GCSTEPSIZE	1024u
#define GCSWEEPMAX	40
#define GCSWEEPCOST	10
#define GCFINALIZECOST	100


#define maskmarks		cast_byte(~(bitmask(BLACKBIT)|WHITEBITS))

#define makewhite(g,x)	\
	((x)->gch.marked = cast_byte(((x)->gch.marked & maskmarks) | luaC_white(g)))

#define white2gray(x)	reset2bits((x)->gch.marked, WHITE0BIT, WHITE1BIT)
#define black2gray(x)	resetbit((x)->gch.marked, BLACKBIT)

#define stringmark(s)	reset2bits((s)->tsv.marked, WHITE0BIT, WHITE1BIT)


#define isfinalized(u)		testbit((u)->marked, FINALIZEDBIT)
#define markfinalized(u)	l_setbit((u)->marked, FINALIZEDBIT)


#define KEYWEAK         bitmask(KEYWEAKBIT)
#define VALUEWEAK       bitmask(VALUEWEAKBIT)



#define markvalue(g,o) { checkconsistency(o); \
	if (iscollectable(o) && iswhite(gcvalue(o))) reallymarkobject(g,gcvalue(o)); }

#define markobject(g,t) { if (iswhite(obj2gco(t))) \
	reallymarkobject(g, obj2gco(t)); }


#define setthreshold(g)  (g->GCthreshold = (g->estimate/100) * g->gcpause)


static void 
removeentry (Node *n)
{
	lua_assert(ttisnil(gval(n)));
	if (iscollectable(gkey(n)))
		setttype(gkey(n), LUA_TDEADKEY);  /* dead key; remove it */
}


static void 
reallymarkobject (global_State *g, GCObject *o) 
{
	lua_assert(iswhite(o) && !isdead(g, o));
	white2gray(o);
	switch (o->gch.tt) 
	{
	case LUA_TSTRING:
		{
			return;
		}
	case LUA_TUSERDATA: 
		{
			Table *mt = gco2u(o)->metatable;
			gray2black(o);  /* udata are never gray */
			if (mt) markobject(g, mt);
			markobject(g, gco2u(o)->env);
			return;
		}
	case LUA_TUPVAL: 
		{
			UpVal *uv = gco2uv(o);
			markvalue(g, uv->v);
			if (uv->v == &uv->u.value)  /* closed? */
				gray2black(o);  /* open upvalues are never black */
			return;
		}
	case LUA_TFUNCTION: 
		{
			gco2cl(o)->c.gclist = g->gray;
			g->gray = o;
			break;
		}
	case LUA_TTABLE: 
		{
			gco2h(o)->gclist = g->gray;
			g->gray = o;
			break;
		}
	case LUA_TTHREAD:
		{
			gco2th(o)->gclist = g->gray;
			g->gray = o;
			break;
		}
	case LUA_TPROTO: 
		{
			gco2p(o)->gclist = g->gray;
			g->gray = o;
			break;
		}
	default: lua_assert(0);
	}
}


static void 
marktmu (global_State *g) 
{
	GCObject *u = g->tmudata;
	if (u) 
	{
		do 
		{
			u = u->gch.next;
			makewhite(g, u);  /* may be marked, if left from previous GC */
			reallymarkobject(g, u);
		} while (u != g->tmudata);
	}
}


/* move `dead' udata that need finalization to list `tmudata' */
size_t
luaC_separateudata (lua_State *L, int all) 
{
	global_State *g = G(L);
	size_t deadmem = 0;
	GCObject **p = &g->mainthread->next;
	GCObject *curr;
	while ((curr = *p) != NULL)
	{
		if (!(iswhite(curr) || all) || isfinalized(gco2u(curr)))
			p = &curr->gch.next;  /* don't bother with them */
		else if (fasttm(L, gco2u(curr)->metatable, TM_GC) == NULL) 
		{
			markfinalized(gco2u(curr));  /* don't need finalization */
			p = &curr->gch.next;
		}
		else 
		{  /* must call its gc method */
			deadmem += sizeudata(gco2u(curr));
			markfinalized(gco2u(curr));
			*p = curr->gch.next;
			/* link `curr' at the end of `tmudata' list */
			if (g->tmudata == NULL)  /* list is empty? */
				g->tmudata = curr->gch.next = curr;  /* creates a circular list */
			else
			{
				curr->gch.next = g->tmudata->gch.next;
				g->tmudata->gch.next = curr;
				g->tmudata = curr;
			}
		}
	}

	return deadmem;
}


static int
traversetable (global_State *g, Table *h)
{
	int i;
	int weakkey = 0;
	int weakvalue = 0;
	const TValue *mode;
	if (h->metatable)
		markobject(g, h->metatable);
	mode = gfasttm(g, h->metatable, TM_MODE);
	if (mode && ttisstring(mode))		 /* is there a weak mode? */
	{ 
		weakkey = (strchr(svalue(mode), 'k') != NULL);
		weakvalue = (strchr(svalue(mode), 'v') != NULL);
		if (weakkey || weakvalue)		/* is really weak? */
		{  
			h->marked &= ~(KEYWEAK | VALUEWEAK);  /* clear bits */
			h->marked |= cast_byte((weakkey << KEYWEAKBIT) |
				(weakvalue << VALUEWEAKBIT));
			h->gclist = g->weak;  /* must be cleared after GC, ... */
			g->weak = obj2gco(h);  /* ... so put in the appropriate list */
		}
	}
	if (weakkey && weakvalue) return 1;
	if (!weakvalue) 
	{
		i = h->sizearray;
		while (i--)
			markvalue(g, &h->array[i]);
	}
	i = sizenode(h);
	while (i--)
	{
		Node *n = gnode(h, i);
		lua_assert(ttype(gkey(n)) != LUA_TDEADKEY || ttisnil(gval(n)));
		if (ttisnil(gval(n)))
			removeentry(n);  /* remove empty entries */
		else
		{
			lua_assert(!ttisnil(gkey(n)));
			if (!weakkey) markvalue(g, gkey(n));
			if (!weakvalue) markvalue(g, gval(n));
		}
	}
	return weakkey || weakvalue;
}


/*
** All marks are conditional because a GC may happen while the
** prototype is still being created
*/
static void 
traverseproto (global_State *g, Proto *f)
{
	int i;
	if (f->source) 
		stringmark(f->source);

	for (i=0; i<f->sizek; i++)  /* mark literals */
		markvalue(g, &f->k[i]);

	for (i=0; i<f->sizeupvalues; i++)	/* mark upvalue names */
	{  
		if (f->upvalues[i])
			stringmark(f->upvalues[i]);
	}

	for (i=0; i<f->sizep; i++)	 /* mark nested protos */
	{ 
		if (f->p[i])
			markobject(g, f->p[i]);
	}

	for (i=0; i<f->sizelocvars; i++)	/* mark local-variable names */
	{  
		if (f->locvars[i].varname)
			stringmark(f->locvars[i].varname);
	}
}



static void 
traverseclosure (global_State *g, Closure *cl) 
{
	markobject(g, cl->c.env);
	if (cl->c.isC) 
	{
		int i;
		for (i=0; i<cl->c.nupvalues; i++)  /* mark its upvalues */
			markvalue(g, &cl->c.upvalue[i]);
	}
	else 
	{
		int i;
		lua_assert(cl->l.nupvalues == cl->l.p->nups);
		markobject(g, cl->l.p);
		for (i=0; i<cl->l.nupvalues; i++)  /* mark its upvalues */
			markobject(g, cl->l.upvals[i]);
	}
}


static void
checkstacksizes (lua_State *L, StkId max)
{
	int ci_used = cast_int(L->ci - L->base_ci);  /* number of `ci' in use */
	int s_used = cast_int(max - L->stack);  /* part of stack in use */
	if (L->size_ci > LUAI_MAXCALLS)  /* handling overflow? */
		return;  /* do not touch the stacks */

	if (4*ci_used < L->size_ci && 2*BASIC_CI_SIZE < L->size_ci)
		luaD_reallocCI(L, L->size_ci/2);  /* still big enough... */
	condhardstacktests(luaD_reallocCI(L, ci_used + 1));
	if (4*s_used < L->stacksize && 2*(BASIC_STACK_SIZE+EXTRA_STACK) < L->stacksize)
		luaD_reallocstack(L, L->stacksize/2);  /* still big enough... */
	condhardstacktests(luaD_reallocstack(L, s_used));
}


static void 
traversestack (global_State *g, lua_State *l) 
{
	StkId o, lim;
	CallInfo *ci;
	markvalue(g, gt(l));
	lim = l->top;
	for (ci = l->base_ci; ci <= l->ci; ci++) 
	{
		lua_assert(ci->top <= l->stack_last);
		if (lim < ci->top) lim = ci->top;
	}
	for (o = l->stack; o < l->top; o++)
		markvalue(g, o);
	for (; o <= lim; o++)
		setnilvalue(o);
	checkstacksizes(l, lim);
}


/*
** traverse one gray object, turning it to black.
** Returns `quantity' traversed.
*/
static l_mem 
propagatemark (global_State *g)
{
	GCObject *o = g->gray;
	lua_assert(isgray(o));
	gray2black(o);
	switch (o->gch.tt)
	{
	case LUA_TTABLE: 
		{
			Table *h = gco2h(o);
			g->gray = h->gclist;
			if (traversetable(g, h))  /* table is weak? */
				black2gray(o);  /* keep it gray */
			return sizeof(Table) + sizeof(TValue) * h->sizearray +
				sizeof(Node) * sizenode(h);
		}
	case LUA_TFUNCTION:
		{
			Closure *cl = gco2cl(o);
			g->gray = cl->c.gclist;
			traverseclosure(g, cl);
			return (cl->c.isC) ? sizeCclosure(cl->c.nupvalues) :
				sizeLclosure(cl->l.nupvalues);
		}
	case LUA_TTHREAD: 
		{
			lua_State *th = gco2th(o);
			g->gray = th->gclist;
			th->gclist = g->grayagain;
			g->grayagain = o;
			black2gray(o);
			traversestack(g, th);
			return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
				sizeof(CallInfo) * th->size_ci;
		}
	case LUA_TPROTO: 
		{
			Proto *p = gco2p(o);
			g->gray = p->gclist;
			traverseproto(g, p);
			return sizeof(Proto) + sizeof(Instruction) * p->sizecode +
				sizeof(Proto *) * p->sizep +
				sizeof(TValue) * p->sizek + 
				sizeof(int) * p->sizelineinfo +
				sizeof(LocVar) * p->sizelocvars +
				sizeof(TString *) * p->sizeupvalues;
		}
	default: lua_assert(0); return 0;
	}
}


static void 
propagateall (global_State *g)
{
	while (g->gray) propagatemark(g);
}


/*
** The next function tells whether a key or value can be cleared from
** a weak table. Non-collectable objects are never removed from weak
** tables. Strings behave as `values', so are never removed too. for
** other objects: if really collected, cannot keep them; for userdata
** being finalized, keep them in keys, but not in values
*/
static int 
iscleared (const TValue *o, int iskey)
{
	if (!iscollectable(o)) return 0;
	if (ttisstring(o)) 
	{
		stringmark(rawtsvalue(o));  /* strings are `values', so are never weak */
		return 0;
	}

	return iswhite(gcvalue(o)) || (ttisuserdata(o) && (!iskey && isfinalized(uvalue(o))));
}


/*
** clear collected entries from weaktables
*/
static void 
cleartable (GCObject *l) 
{
	while (l) 
	{
		Table *h = gco2h(l);
		int i = h->sizearray;
		lua_assert(testbit(h->marked, VALUEWEAKBIT) ||
			testbit(h->marked, KEYWEAKBIT));
		if (testbit(h->marked, VALUEWEAKBIT)) 
		{
			while (i--) 
			{
				TValue *o = &h->array[i];
				if (iscleared(o, 0))  /* value was collected? */
					setnilvalue(o);  /* remove value */
			}
		}
		i = sizenode(h);
		while (i--) 
		{
			Node *n = gnode(h, i);
			if (!ttisnil(gval(n)) &&  /* non-empty entry? */
				(iscleared(key2tval(n), 1) || iscleared(gval(n), 0)))
			{
				setnilvalue(gval(n));  /* remove value ... */
				removeentry(n);  /* remove entry from table */
			}
		}
		l = h->gclist;
	}
}


static void 
freeobj (lua_State *L, GCObject *o) 
{
	switch (o->gch.tt) 
	{
	case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
	case LUA_TFUNCTION: luaF_freeclosure(L, gco2cl(o)); break;
	case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
	case LUA_TTABLE: luaH_free(L, gco2h(o)); break;
	case LUA_TTHREAD:
		{
			lua_assert(gco2th(o) != L && gco2th(o) != G(L)->mainthread);
			luaE_freethread(L, gco2th(o));
			break;
		}
	case LUA_TSTRING:
		{
			G(L)->strt.nuse--;
			luaM_freemem(L, o, sizestring(gco2ts(o)));
			break;
		}
	case LUA_TUSERDATA:
		{
			luaM_freemem(L, o, sizeudata(gco2u(o)));
			break;
		}
	default: lua_assert(0);
	}
}



#define sweepwholelist(L,p)	sweeplist(L,p,MAX_LUMEM)


static GCObject **
sweeplist (lua_State *L, GCObject **p, lu_mem count) 
{
	GCObject *curr;
	global_State *g = G(L);
	int deadmask = otherwhite(g);
	while ((curr = *p) != NULL && count-- > 0) 
	{
		if (curr->gch.tt == LUA_TTHREAD)  /* sweep open upvalues of each thread */
			sweepwholelist(L, &gco2th(curr)->openupval);
		if ((curr->gch.marked ^ WHITEBITS) & deadmask)	 /* not dead? */
		{ 
			lua_assert(!isdead(g, curr) || testbit(curr->gch.marked, FIXEDBIT));
			makewhite(g, curr);  /* make it white (for next cycle) */
			p = &curr->gch.next;
		}
		else	/* must erase `curr' */
		{  
			lua_assert(isdead(g, curr) || deadmask == bitmask(SFIXEDBIT));
			*p = curr->gch.next;
			if (curr == g->rootgc)  /* is the first element of the list? */
				g->rootgc = curr->gch.next;  /* adjust first */
			freeobj(L, curr);
		}
	}
	return p;
}


static void 
checkSizes (lua_State *L) 
{
	global_State *g = G(L);
	/* check size of string hash */
	if (g->strt.nuse < cast(lu_int32, g->strt.size/4) &&
		g->strt.size > MINSTRTABSIZE*2)
		luaS_resize(L, g->strt.size/2);  /* table is too big */
	/* check size of buffer */
	if (luaZ_sizebuffer(&g->buff) > LUA_MINBUFFER*2)	  /* buffer too big? */
	{
		size_t newsize = luaZ_sizebuffer(&g->buff) / 2;
		luaZ_resizebuffer(L, &g->buff, newsize);
	}
}


static void 
GCTM (lua_State *L) 
{
	global_State *g = G(L);
	GCObject *o = g->tmudata->gch.next;  /* get first element */
	Udata *udata = rawgco2u(o);
	const TValue *tm;
	/* remove udata from `tmudata' */
	if (o == g->tmudata)  /* last element? */
		g->tmudata = NULL;
	else
		g->tmudata->gch.next = udata->uv.next;
	udata->uv.next = g->mainthread->next;  /* return it to `root' list */
	g->mainthread->next = o;
	makewhite(g, o);
	tm = fasttm(L, udata->uv.metatable, TM_GC);
	if (tm != NULL) 
	{
		lu_byte oldah = L->allowhook;
		lu_mem oldt = g->GCthreshold;
		L->allowhook = 0;  /* stop debug hooks during GC tag method */
		g->GCthreshold = 2*g->totalbytes;  /* avoid GC steps */
		setobj2s(L, L->top, tm);
		setuvalue(L, L->top+1, udata);
		L->top += 2;
		luaD_call(L, L->top - 2, 0);
		L->allowhook = oldah;  /* restore hooks */
		g->GCthreshold = oldt;  /* restore threshold */
	}
}


/*
** Call all GC tag methods
*/
void
luaC_callGCTM (lua_State *L)
{
	while (G(L)->tmudata)
		GCTM(L);
}


void 
luaC_freeall (lua_State *L)
{
	global_State *g = G(L);
	int i;
	g->currentwhite = WHITEBITS | bitmask(SFIXEDBIT);  /* mask to collect all elements */
	sweepwholelist(L, &g->rootgc);
	for (i = 0; i < g->strt.size; i++)  /* free all string lists */
		sweepwholelist(L, &g->strt.hash[i]);
}


static void
markmt (global_State *g)
{
	int i;
	for (i=0; i<NUM_TAGS; i++)
		if (g->mt[i]) markobject(g, g->mt[i]);
}


/* mark root set */
static void 
markroot (lua_State *L)
{
	global_State *g = G(L);
	g->gray = NULL;
	g->grayagain = NULL;
	g->weak = NULL;
	markobject(g, g->mainthread);
	/* make global table be traversed before main stack */
	markvalue(g, gt(g->mainthread));
	markvalue(g, registry(L));
	markmt(g);
	g->gcstate = GCSpropagate;
}


static void 
remarkupvals (global_State *g) 
{
	UpVal *uv;
	for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next)
	{
		lua_assert(uv->u.l.next->u.l.prev == uv && uv->u.l.prev->u.l.next == uv);
		if (isgray(obj2gco(uv)))
			markvalue(g, uv->v);
	}
}


static void 
atomic (lua_State *L) 
{
	global_State *g = G(L);
	size_t udsize;  /* total size of userdata to be finalized */
	/* remark occasional upvalues of (maybe) dead threads */
	remarkupvals(g);
	/* traverse objects cautch by write barrier and by 'remarkupvals' */
	propagateall(g);
	/* remark weak tables */
	g->gray = g->weak;
	g->weak = NULL;
	lua_assert(!iswhite(obj2gco(g->mainthread)));
	markobject(g, L);  /* mark running thread */
	markmt(g);  /* mark basic metatables (again) */
	propagateall(g);
	/* remark gray again */
	g->gray = g->grayagain;
	g->grayagain = NULL;
	propagateall(g);
	udsize = luaC_separateudata(L, 0);  /* separate userdata to be finalized */
	marktmu(g);  /* mark `preserved' userdata */
	propagateall(g);  /* remark, to propagate `preserveness' */
	cleartable(g->weak);  /* remove collected objects from weak tables */
	/* flip current white */
	g->currentwhite = cast_byte(otherwhite(g));
	g->sweepstrgc = 0;
	g->sweepgc = &g->rootgc;
	g->gcstate = GCSsweepstring;
	g->estimate = g->totalbytes - udsize;  /* first estimate */
}


static l_mem 
singlestep (lua_State *L) 
{
	global_State *g = G(L);
	/*lua_checkmemory(L);*/
	switch (g->gcstate)
	{
	case GCSpause: 
		{
			markroot(L);  /* start a new collection */
			return 0;
		}
	case GCSpropagate:
		{
			if (g->gray)
				return propagatemark(g);
			else {  /* no more `gray' objects */
				atomic(L);  /* finish mark phase */
				return 0;
			}
		}
	case GCSsweepstring: 
		{
			lu_mem old = g->totalbytes;
			sweepwholelist(L, &g->strt.hash[g->sweepstrgc++]);
			if (g->sweepstrgc >= g->strt.size)  /* nothing more to sweep? */
				g->gcstate = GCSsweep;  /* end sweep-string phase */
			lua_assert(old >= g->totalbytes);
			g->estimate -= old - g->totalbytes;
			return GCSWEEPCOST;
		}
	case GCSsweep: 
		{
			lu_mem old = g->totalbytes;
			g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
			if (*g->sweepgc == NULL) {  /* nothing more to sweep? */
				checkSizes(L);
				g->gcstate = GCSfinalize;  /* end sweep phase */
			}
			lua_assert(old >= g->totalbytes);
			g->estimate -= old - g->totalbytes;
			return GCSWEEPMAX*GCSWEEPCOST;
		}
	case GCSfinalize: 
		{
			if (g->tmudata) 
			{
				GCTM(L);
				return GCFINALIZECOST;
			}
			else 
			{
				g->gcstate = GCSpause;  /* end collection */
				g->gcdept = 0;
				return 0;
			}
		}
	default: lua_assert(0); return 0;
	}
}


void 
luaC_step (lua_State *L)
{
	global_State *g = G(L);
	l_mem lim = (GCSTEPSIZE/100) * g->gcstepmul;
	if (lim == 0)
		lim = (MAX_LUMEM-1)/2;  /* no limit */
	g->gcdept += g->totalbytes - g->GCthreshold;
	do 
	{
		lim -= singlestep(L);
		if (g->gcstate == GCSpause)
			break;
	} while (lim > 0);
	if (g->gcstate != GCSpause) 
	{
		if (g->gcdept < GCSTEPSIZE)
			g->GCthreshold = g->totalbytes + GCSTEPSIZE;  /* - lim/g->gcstepmul;*/
		else
		{
			g->gcdept -= GCSTEPSIZE;
			g->GCthreshold = g->totalbytes;
		}
	}
	else
	{
		lua_assert(g->totalbytes >= g->estimate);
		setthreshold(g);
	}
}


void
luaC_fullgc (lua_State *L) 
{
	global_State *g = G(L);
	if (g->gcstate <= GCSpropagate)
	{
		/* reset sweep marks to sweep all elements (returning them to white) */
		g->sweepstrgc = 0;
		g->sweepgc = &g->rootgc;
		/* reset other collector lists */
		g->gray = NULL;
		g->grayagain = NULL;
		g->weak = NULL;
		g->gcstate = GCSsweepstring;
	}
	lua_assert(g->gcstate != GCSpause && g->gcstate != GCSpropagate);
	/* finish any pending sweep phase */
	while (g->gcstate != GCSfinalize)
	{
		lua_assert(g->gcstate == GCSsweepstring || g->gcstate == GCSsweep);
		singlestep(L);
	}
	markroot(L);
	while (g->gcstate != GCSpause)
	{
		singlestep(L);
	}
	setthreshold(g);
}


void 
luaC_barrierf (lua_State *L, GCObject *o, GCObject *v)
{
	global_State *g = G(L);
	lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
	lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
	lua_assert(ttype(&o->gch) != LUA_TTABLE);
	/* must keep invariant? */
	if (g->gcstate == GCSpropagate)
		reallymarkobject(g, v);  /* restore invariant */
	else  /* don't mind */
		makewhite(g, o);  /* mark as white just to avoid other barriers */
}


void
luaC_barrierback (lua_State *L, Table *t) 
{
	global_State *g = G(L);
	GCObject *o = obj2gco(t);
	lua_assert(isblack(o) && !isdead(g, o));
	lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
	black2gray(o);  /* make table gray (again) */
	t->gclist = g->grayagain;
	g->grayagain = o;
}


void 
luaC_link (lua_State *L, GCObject *o, lu_byte tt)
{
	global_State *g = G(L);
	o->gch.next = g->rootgc;
	g->rootgc = o;
	o->gch.marked = luaC_white(g);
	o->gch.tt = tt;
}


void 
luaC_linkupval (lua_State *L, UpVal *uv) 
{
	global_State *g = G(L);
	GCObject *o = obj2gco(uv);
	o->gch.next = g->rootgc;  /* link upvalue into `rootgc' list */
	g->rootgc = o;
	if (isgray(o))
	{ 
		if (g->gcstate == GCSpropagate) 
		{
			gray2black(o);  /* closed upvalues need barrier */
			luaC_barrier(L, uv, uv->v);
		}
		else	/* sweep phase: sweep it (turning it into white) */
		{  
			makewhite(g, o);
			lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
		}
	}
}

